1. Marie-Noëlle HOUSSAIS
Mechanisms driving the interannual variability of the Canadian Arctic Archipelago outflow
Christophe HERBAUT
Marie-Noëlle HOUSSAIS
LOCEAN/IPSL, PARIS

2. Variability of the CAA outflow (observations)
Lancaster Sound
Correlation to NAO
Melling et al., 2008

3. Arctic fresh water content (annual mean, S<34.8)
Simulated ( )
PHC 3

4. Arctic fresh water content (ctd.)
EOF analysis : leading modes

5. AOMIP Workshop WHOI 21-23 October 2009
Fresh water content and NAO
NAO leads NAO lags
PC1
PC2
PC3
AOMIP Workshop WHOI October 2009

6. What controls the variability of the FW export through the CAA ?
Link to the atmospheric forcing
Link to the Arctic FW reservoir

7. Arctic – North Atlantic model (NEMO/ORCA05)
Regional Configuration ORCA05: Arctic+ Atlantic ( 30°S):
résolution : ~20-25 km in the Arctic
46 vertical levels, partial steps
Sea ice model
LIM2 (Hibler 1979 two-level sea ice model)
Viscous plastic rheology
3 layers thermodynamics
Forcings
Atmospheric forcing :ERA40 reanalysis ( )
Relaxation on climatological SSS (trelax= 30 days)
Open boundaries at 30°S (Atlantic) and 50°N (Pacific) :monthly climatological T, S, u from global simulation

8. Canadian Arctic Archipelago outflow
Closed straits :
- Cardigan Strait + Hell Gate
- Fury and Hecla Strait
Arctic Ocean outflow
Inflow to Baffin Bay
Nares Strait
Smith Sound
McClure Strait
Amundsen Gulf
Byam Martin Channel + Penny Strait
Lancaster Sound

9. Fresh water export through the CAA
Annual mean
Volume (Sv)
Fresh water (mSv)
Liquid Smith
1.3 70
Liquid Lancaster
1.1 90
Liquid total CAA
2.4
160
Ice
(liquid equ.) 5

10. Fresh water export through the CAA
Relative contributions of velocity and salinity anomalies
Normalized transports
Volume transport CAA
FW transport Davis Strait (S<34.6)

11. Outflow to Lancaster Sound
McClure
Byam Martin
Penny
Amundsen

12. AOMIP Workshop WHOI 21-23 October 2009
Subsurface velocity anomalies in McClure Strait
Cross-strait velocity regressed on Lancaster outflow
AOMIP Workshop WHOI October 2009

13. Regression on Lancaster outflow
Bifurcation of the boundary current in Mc Clure Strait
Current velocity at 110 m
Climatology
Regression
on Lancaster outflow
McClure

14. Upstream and downstream forcing on Lancaster outflow
Correlation Lancaster outflow with:
. SSH McClure-SSH Lancaster
. SSH McClure
. SSH Lancaster

15. SSH forcing on Lancaster outflow
SSH climatology
SSH on SSH in McClure

16. Downstream forcing on Nares Srait outflow
Correlation Nares outflow with SSH
SSH Nares-SSH Smith
SSH Nares
SSH Smith

17. Subpolar SSH forcing on Nares Strait transport
SSH regressed on transport in Nares Strait
SSH regressed on SSH in Smith Sound
Unsignificant SSH forcing in central Arctic

18. Wind driven SSH variability in the Arctic
Ekman drift regressed on Lancaster outflow
Accumulation of the Ekman flow against the CAA coast

19. Mechanisms of SSH variability in Baffin Bay
Air-sea heat flux on SSH in Smith Sound
 Lagged response of Baffin Bay to buoyancy driven SSH changes in the Labrador Sea

20. Atmospheric modes driving CAA variability
SLP on
SSH in Smith Sound
SLP on
Lancaster outflow
 NAO-like SLP patterns

21. Response to NAO-like atmospheric forcing
 Arctic/subpolar influence on CAA outflow
 Wind stress/buoyancy forcing on CAA outflow
SLP
Idealized experiments :
Construct NAO+ composites of NDJFM forcing fields
10-year experiments with repeated annual cycle of composite forcing

22. Idealized experiments
3 sensitivity experiments :
Wind stress
Buoyancy forcing (SAT and SHU)
Buoyancy forcing restricted to south of Davis and GISR
NAO wind stress
NAO heat flux

23. SSH anomalies in idealized experiments
Buoyancy
Atlantic
Wind
Buoyancy
Wind driven Arctic SSH anomalies : same pattern as SSH pattern impacting on McClure Strait
Buoyancy driven subpolar anomalies : same pattern as SSH pattern impacting on Nares Strait

24. Time evolution of the response
Distribution between passages
Total CAA outflow
WIND
BUOYANCY
BUOYANCY_ATL
--- Nares Strait
__ Lancaster Sound

25. Link to arctic fresh water content (FWC)
Correlation PC3-Lancaster
Regression FWC on Lancaster outflow
FW content - EOF3

26. Summary
The fresh water outflow through the CAA is mainly controlled by volume transports, in agreement with observations.
Both ouflows to Lancaster and Smith sounds correlate high (~0.8) with the along channel SSH difference (Jahn et al., 2009).
However distinct mechanisms :
Lancaster Sound : largely controlled by the SSH variability at the periphery of the Beaufort Gyre  slowing-down of the boundary current north of the CAA  more water to McClure
Smith Sound : primarily controlled by the downstream SSH variability in Baffin Bay
Both channels respond to the dominant mode of the winter atmosphere variability (Condron et al., 2009):
SSH in the Arctic : local convergence of the Ekman drift against the CAA
SSH in Baffin Bay : lagged response to buoyancy forcing in the Labrador Sea.
SSH forcing in McClure not directly linked to the leading modes of variability of the Arctic FW content (variations of thickness and extent of the Beaufort Gyre FW reservoir) but rather to a regional redistribution of the FW north of the Archipelago